Thread difference between BSPT, BSPP & NPT
Different thread sealing depending on the geographical region, size of the pressure system, and the environment. For example, In Asia, such as China, Korea, Japan, etc normally use BSPT; In U.S, Canada, etc always use NPT, then the BSPP thread is most popular in UK, Europe, Australia, New Zealand, and South Africa. While one sealing style is not inherently better than another each style has its application.
NPT Connections ( National Pipe Thread)- US & Canada
It is according to ANSI/ASME B1.20.1 Pipe Threads. 60 degrees of thread angle. NPT male adapters have a taper thread that wedges into the female NPT adapter.